Due to advances in recombinant DNA technology, technologies have been developed that obtain the target gene product by making a foreign gene express itself in a host such as a microbe, mold, animal, plant, or insect, and growing the gene's transformant. For example, by culturing yeast or the like, it is possible to produce a large volume of target gene product through fermentation production.
There have been several attempts to produce L-lactic acid using yeast. There have also been attempts to produce L-lactic acid by incorporating a bovine lactate dehydrogenase (LDH) gene into Saccaromyces cerevisiae (Eri Adhi et al., “Modification of metabolic pathway of Saccaromyces cerevisiae by the expression of lactate dehydrogenase and deletion of pyruvate genes for the lactic acid fermentation at low pH value,” J. Ferment. Bioeng. Vol. 86, No. 3, 284-289, 1988; Danio Porro et al., “Development of metabolically engineered Saccaromyces cerevisiae cells for the production of lactic acid,” Biotechnol. Prog. Vol. 11, 294-298, 1995, Kohyo (Japanese unexamined patent publication) No. 2001-516584). However, high-volume production of L-lactic acid was not observed in either of these reports.
It is known that the pyruvate decarboxylase in Saccaromyces cerevisiae has multiple isozymes. In ordinary yeast, pyruvate decarboxylase 1 is functioning. However, if this protein does not express itself due to the destruction of the main gene, etc., pyruvate decarboxylase 5 functions, thus maintaining ethanol production (“Autoregulation of yeast pyruvate decarboxylase gene expression requires the enzyme but not its catalytic activity,” Ines Eberhardt, Hakan Cederberg, Haijuan Li, Stephen Koning, Frank Jordan and Stephen Hohmann, Eur. J. Biochem. Vol. 262, 191-201, 1999).